I bought two consecutive (seemingly) identical sets, which, however, are actually no-name.
In the first one, the LED of the small component burned out after the first five (!) measurements, rendering the set useless for Ethernet cable testing.
The second set is functioning properly so far.
I rate the product with 2 stars because I believe it's a matter of luck whether you'll get a piece that works properly or not.

If you need it for professional use, I would recommend buying a branded product.